Spray refining



United States Patent Malvern John Rhydderch Firbeck, near Worksop, England 640,121

May 22, 1967 Nov. 24, 1970 The British Iron and Steel Research Association May 23, 1966, July 5, 1966 Great Britain Nos. 22790/66 and 30198/66 Inventor Appl. No. Filed Patented Assignee Priority SPRAY REFINING 7 Claims, 4 Drawing Figs.

266/34 B051) 1/26 Field ofSearch 266/34, 35, 34.1, 34.2, 34PP, 34PT, 341', 41, 38;?5/51, 52,

[56] References Cited UNITED STATES PATENTS 2,969,282 1/1961 Churcher 75/52X 3,201,105 8/1965 Miller 266/34 3,251,680 5/1966 Goss et al. 266/34(T)UX 3,260,591 7/1966 Brown et al.... 75/93X 3,356,489 12/1967 Feichtinger 266/34X 1,856,679 5/1932 Williams etal. .1 18/2.5(M)UX 2,968,062 1/1961 Probstet al 18/2.5(M)UX 3,021,558 2/1962 Roberson 239/433X Primary Examiner-J. Spencer Overholser Assistant Examiner-John S. Brown Attorney- Holcombe, Wetherill & Brisebois ABSTRACT: A method and apparatus for refining metal in which a thin wide stream of molten metal is fed to a vessel when it is shattered by streams of oxidising gas directed at the major faces of the stream.

Patented Nov. 24, 1970 3,542,351

Shnet of 2 INVENTOR M. J'. Ravaos'mu LJ EL WAMH M ck ATTORNEYS Sheet 2 of 2 I INVENTOR VLJ'. RHYDDE'RCH ATTORNEYS SPRAY nsrmrno I This invention is concerned with improvements in and relating to refining of metal by oxidising impurity therein.

In our United Kingdom Letters Pat. Nos. 809282, 949610 and 1,006,082 there is described a process for reducing impurity in ferrous metal comprising establishing a stream of molten metal and shattering the stream into droplets by a jet of oxidising gas. This process is referred to as spray refining.

It has been proposed to form the stream as a cylindrical stream and to break up the stream with radially inwardly directed convergentjets of oxidising gas.

However such a process is completely satisfactory only for small flow rates of metal, say 0.2tons/minQwith a five-eighths 1 1 inch diameter stream. To obtain higher throughput the diameter of the stream can be'increased but the surface area to volume per unit length of the stream exposed to the oxidising gas decreases as the diameter is increased and refining is less efficient because more oxygen is required to achieve the necessary shattering of the stream. Therefore the higher flow rate required, the larger the diameter of stream and the greater the quantity of oxygen per ton of metal. The upper limit of size ofa cylindrical stream is 1 /2 inches which in practice means a flow rate of 1 ton per minute.

In an attempt to achieve increased throughput with efficient oxygen usage it has been proposed in our Pat. No. 1,006,082

to provide an annular stream to increase the surface area to volume ratio per unit length of stream and an annulus of 6 inches diameter may be used. However the high surface tension on both the inner and outer surfaces of the annulus tends to draw the annular stream into a solid stream which counteracts the benefit ofthe greater surface area to volume ration per unit length. Thelnaximum throughput is relatively low say 2.5 tons per minute.

There is however a possibility for much greater throughput treating the iron. The treated iron .will melt the scrap by the rates and it is an object ofthe invention to provide a method of refining iron at rates substantially higher than hitherto whilst obtaining an efficient use ofthe oxidising gas.

According to the present invention there is provided a method of refining a molten metal comprising forming a flow thereof which in a plane normal to the direction of flow has in a first direction a dimension several times greater than the dimension in a second direction normal to the first, and shattering the flow with a stream of oxidising gas to thereby oxidise the impurity to be removed.

The flow may be of any suitable form such as a coherent stream of rectangular or elliptical sectionprovided always that the flow has a high surface to volume ration per unit length of stream.

The metal may be discharged as a freely falling coherent stream from a tundish, the stream being ofthe order of onehalf inch thick and 3 inches wide which will give, with a 14 inch head of molten iron, a flow rate'of 1 ton per minute. When molten iron is thus pouredand shattered by the oxidising gas the metalloid content can be reduced to acceptable levels for the finished steel;

A stream may however by substantially larger in width, say 24 inch wide and one-half inch thick to provide a throughput, with a 14inch head ofmolten iron of8 tons per minute.

13y adoption ofthis thin wide geometry offlow, the oxidising gas utilisation per ton of metal is directly related to the major dimension ofthe stream and hence flow rate of the metal.

Thus for refining iron containing 4 percent carbon, 2 per cent silicon, 1 percent manganese, 0.15 percent phosphorus and 0.04 percent sulphur, the metal can be poured through an outlet one-half inch by 1 /2 inches at 0.5 tons/minute and refined with oxygen at 2,400 cu.ft./ton to produce a material containing 0.02 percent carbon, 0.01 percent silicon, 0.01 percent manganese, 0.015 percent phosphorus and 0.01 percent sulphur. If a throughput of 2 tons per minute is required the stream is formed as one-half inch by 6 inches and the ox ygen required will still be 2,400 cu.ft./ton of metal.

The refined material may be collected in a receiving vessel which may be charged with a suitable amount of scrap prior to completion of the pour of hot metal. Alternatively, scrap and/or prereduced or partially reduced iron ore pellets may be fed into the receiving vessel during the time that the iron is being refined. Such additions may be made intermittently or continuously. It is a particularly advantageous feature of this invention that prereduced or partially reduced pellets are used as coolant in the treatment of liquid iron because they can be supplied in regular and controllable fashion, which is not so easily done with a scrap steel and iron.

Alternatively the iron may be treated in more than one stage. For example, the first stage will desiliconise and partly decarburise the iron and the metal may then be passed to a second stage in which it is poured as a thin wide flow past further oxygenjets to remove further impurities.

The desiliconising stage may alternatively be used as a source of-prerefined material for steel production in another vessel, say an L.D. converter. The metal treated in such a desiliconising stage can either be received in a separate vessel, or the L.D. converter or other steelmaking unit may be used as a receiving vessel in the first stage, an oxygen lance being lowered into the vessel after the first stage to complete the steelmaking process.

The usual fluxes may be fed as a curtain beside each wide face of the metal flow before it reaches the oxidising gas streams and these gas streams are preferably in the form of laminar jets of gas whose paths would intersect in the metal stream.

To carry out the method according to the invention there is provided apparatus comprising a container for molten metal having a discharge nozzle defining a passage of a shape to produce a metal flow which has in a first direction normal to the direction. of flow a dimension several times greater than the dimension in a second direction normal to the first direction and to the flow, and conduits located relative to the path of the flow for discharging a gas into that path to shatter the flow.

The conduits defining the gas outlets preferably have a convergent divergent axial section to accelerate the gas and preferably form two curtains of gas each of the same width as the metal stream.

In order that the present'invention may be well understood there will now be described on embodiment of apparatus, given by way of example only, reference being bad to the accompanying drawing in which:

FIG. 1 is a plan view of a gas discharge device;

FIG. 2 is a section on the'line 11-11 of FIG. 1;

FIG. 3 is a side elevation, and

FIG. 4 is a diagrammatic section of a refining plant.

The gas discharge device is located below a refractory nozzle set in a tundish. The nozzle is shown at 1 in chain-dot line in FIGS. 1, 2 and 3, although it would be above the plane of the paper in FIG. 1. The gas discharge device comprises a header 2, with an inlet 3 and two takeoff chambers 4 having gas discharge conduits 5 as wide as the larger dimension of the passage defined by the refractory nozzle. The walls of each discharge conduit converge and diverge as shown in FIG. 2 to accelerate the gas, and the discharge conduits are angled so that the path of a curtain of gas produced by one conduit intersects the path ofa curtain of gas produced by the other conduit in the metal stream. The smaller dimension of each discharge conduit at this outlet may be of the order of 0.1 inch. A flux discharge device is shown diagrammatically in FIG. 2 having a container 6 on each side of the nozzle outlet, each provided with a gas and flux inlet 7 and an angled discharge outlet 8 to produce a curtain of flux 9 adjacent each major face of the stream of metal when issuing from the nozzle.

Referring to FIG. 4 there is shown a transfer ladle 10 having a flow control stopper 11 for controlling the feed of metal to a tundish 12 of which the outlet is provided with a refractory nozzle as in FIGS. 1 to 3. The nozzle discharges into a receiving vessel 13 located under a hood 14 from which .a fume extractor pipe 15 extends. Between the hood and vessel is an air gap 16. A chute 17, for coolant addition, is provided. ln operation with metal discharging through the nozzle and the oxygen jets impinging on the metal stream, the stream is atomised and the metalloid content is oxidised An extractor draws fume from the hood and as result air is drawn in through the gap 16. In the case of refining ferrous metal this air burns the carbon monoxide formed by the primary oxidation of carbon so that the quantity of blown oxygen is less than that required to fully oxidise the impurity to be removed.

I claim:

1. Apparatus for refining molten metal comprising a container for the molten metal and nozzle means supplied by said container and fromiwhich the metal will fall freely and vertiically under the influence of gravity. said nozzle means being shaped and positioned to direct the flow of said molten metal therefrom into a vertical path having, in a first horizontal direction, a dimension several times greater than its dimension in a second horizontal direction atright angles to said first direction, and means for discharging only against at least one of those sides of said metal flow path which extend in said first direction, and in at least one path extending across the full width ofsaid metal flow path, a gas capable of reacting with an impurity to be removed from the metal.

2. Apparatus according to claim 1, wherein the nozzle means is such as to discharge a metal flow comprising a coherent stream which in section in a plane normal to the direction of flow has opposite sides of a dimension several times the mean distance'between those sides.

3. Apparatus according to claim 1, wherein the nozzle means defines a passage of rectangular cross section.

4. Apparatus accordingto claim i, wherein the nozzle means defines a passage of elliptical cross section.

5. Apparatus according to claim 1, wherein the gas discharge means comprises conduits located on each side of the major-dimension of the metal flow path, the conduits being such as to discharge gas flows which will intersect the metal flow path at a common impact zone.

6. Apparatus according to claim 1, wherein the gas discharge meanshas a convergent/divergent outlet means to accelerate flow of gas therethrough.

7. Apparatus for refining molten metal comprising a container for the moltenmetal and nozzle means supplied by said .container and from which the metal will fall freely and vertically under the influence of gravity. said nozzle means being shaped and positioned to direct the flow of said molten metal therefrom into a vertical path having. in a first horizontal direction, a dimension several times greater than its dimension in a second horizontal direction at right angles to said first direction, means for discharging only against at least one of those sides of said metal flow path which extend in said first direction, and in at least one path extending across the full width of said metal flow path, a gas capable of reacting with an impurity to be removed from the metal, and means for discharging a curtain of flux along at least one side of the metal flow path extending in said first direction. 

